Temporary adhesive composition, and method of producing thin wafer

ABSTRACT

A temporary adhesive for which temporary adhesion is simple and subsequent detachment is also simple, meaning productivity can be improved. Also, a method of producing a thin wafer that uses the temporary adhesive. The temporary adhesive composition comprises:
     (A) an organopolysiloxane comprising:
       (I) 40 to 99 mol % of siloxane units represented by R 1 SiO 3/2  (T units),   (II) 0 to 49 mol % of siloxane units represented by R 2 R 3 SiO 2/2  units (D units) and   (III) 1 to 25 mol % of siloxane units represented by R 4 R 5 R 6 SiO 1/2  units (M units)
 
(wherein each of R 1  to R 6  represents an unsubstituted or substituted monovalent hydrocarbon group of 1 to 10 carbon atoms),
   and having a weight-average molecular weight exceeding 2,000, and   
       (B) an organic solvent having a boiling point of not more than 220° C.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a temporary adhesive composition which,by heating, is able to control the bonding between substrates, bondingbetween a substrate and a support, and the detachment of items that havebeen bonded together. The invention also relates to a method ofproducing a thin wafer that uses the adhesive.

2. Description of the Prior Art

Three-dimensional semiconductor mounting has become an essential processfor achieving increased packing densities and higher capacities. Thethree-dimensional mounting technique is a semiconductor fabricationtechnique in which single semiconductor chips are reduced in thicknessto form thin chips, and a plurality of layers of these chips are thenstacked together with through-silicon vias (TSV) used for electricalconnections between the layers. In order to realize this type ofstructure, a substrate having a semiconductor circuit formed thereonmust be subjected to grinding of the non-circuit-formed surface (alsoreferred to as the “back surface”) to reduce the thickness of thesubstrate, and electrodes including TSVs must then be formed on the backsurface. During the back surface grinding of the silicon substrate, aprotective tape is bonded to the opposite side of the substrate to thegrinding surface, thereby preventing wafer breakage during grinding.However, this tape uses an organic resin film as the base materialwhich, although exhibiting good flexibility, suffers from inadequatestrength and heat resistance, meaning it is not suited to the subsequentback surface wiring layer formation process.

Accordingly, a system has been proposed in which the semiconductorsubstrate is bonded to a support of silicon or glass or the like usingan adhesive, thereby achieving a structure that is able tosatisfactorily withstand both the back surface grinding and the backsurface electrode formation steps. In this system, the adhesive usedwhen bonding the substrate to the support is an important factor. Theadhesive must be capable of bonding the substrate to the support with novoids therebetween, have sufficient durability to withstand thesubsequent processing steps, and then finally, must allow the thin waferto be easily detached from the support. Because this detachment isperformed in the final step, in this description, the adhesive is termeda “temporary adhesive”.

Conventional temporary adhesives and detachment methods that have beenproposed include a technique in which an adhesive containing alight-absorbing substance is irradiated with high-intensity light,thereby decomposing the adhesive layer and enabling the adhesive layerto be detached from the support (Patent Document 1:US 2005/0233547 A1),and a technique in which a heat-meltable hydrocarbon-based compound isused as the adhesive, and bonding and detachment are both performed withthe adhesive in a heated and melted state (Patent Document 2: JP2006-328104 A). The former technique requires expensive equipment suchas a laser or the like, and also suffers from the problem that theprocessing time per substrate is long. Although the latter technique iscontrolled solely be heating, and is therefore relatively simple, theheat stability of the hydrocarbon-based compound at high temperaturesexceeding 200° C. is inadequate, meaning the applicable temperaturerange is narrow.

Further, a technique that uses a silicone pressure-sensitive adhesive asthe temporary adhesive has also been proposed (Patent Document 3: U.S.Pat. No. 7,541,264). In this technique, the substrate is bonded to asupport using an addition reaction-curable silicone pressure-sensitiveadhesive, and then at the time of detachment, the structure is immersedin a chemical agent that dissolves or decomposes the silicone resin,enabling the substrate to be detached from the support. However, thisdetachment requires an extremely long period of time, making itdifficult to apply the technique to an actual production process.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: US 2005/0233547 A1-   Patent Document 2: JP 2006-328104 A-   Patent Document 3: U.S. Pat. No. 7,541,264

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide atemporary adhesive for which temporary adhesion is simple and subsequentdetachment is also simple, meaning productivity can be improved, andalso to provide a method of producing a thin wafer that uses thetemporary adhesive.

The inventors of the present invention discovered that a compositioncomposed of an organopolysiloxane and an organic solvent that acts as adiluting solvent was effective in achieving the above object.

In other words, the present invention provides a temporary adhesivecomposition comprising:

(A) an organopolysiloxane comprising:

(I) 40 to 99 mol % of siloxane units represented by R¹SiO_(3/2) (Tunits),

(II) 0 to 49 mol % of siloxane units represented by R²R³SiO_(2/2) units(D units) and

(III) 1 to 25 mol % of siloxane units represented by R⁴R⁵R⁶SiO_(1/2)units (M units) (wherein each of R¹ to R⁶ represents an unsubstituted orsubstituted monovalent hydrocarbon group of 1 to 10 carbon atoms),

and having a weight-average molecular weight exceeding 2,000, and

(B) an organic solvent having a boiling point of not more than 220° C.

With the temporary adhesive of the present invention, bonding anddetachment can be controlled by heating. The temporary adhesive can bondtwo target items together at a temperature of not more than 200° C., butalso exhibits excellent thermal stability at temperatures of 200° C. orhigher. The method of producing a thin wafer according to the presentinvention that uses the above-mentioned temporary adhesive exhibitsexcellent productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration describing a detachment test methodused in the examples.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A more detailed description of the present invention is presented below.

<Temporary Adhesive Composition> —(A) Organopolysiloxane—

The organopolysiloxane of the component (A) is essentially unreactive,and comprises 40 to 99 mol %, and preferably 50 to 95 mol %, of siloxaneunits represented by R¹SiO_(3/2) (T units), 0 to 49 mol %, andpreferably 10 to 40 mol %, of siloxane units represented byR²R³SiO_(2/2) units (D units), and 1 to 25 mol %, and preferably 3 to 20mol %, of siloxane units represented by R⁴R⁵R⁶SiO_(1/2) units (M units).

In the above-mentioned units, each of the organic substituents R¹, R²,R³, R⁴, R⁵ and R⁶ represents an unsubstituted or substituted monovalenthydrocarbon group of 1 to 10 carbon atoms, and specific examples includehydrocarbon groups, including alkyl groups such as a methyl group, ethylgroup, vinyl group, n-propyl group, isopropyl group, n-butyl group,t-butyl group, n-pentyl group and n-hexyl group, cycloalkyl groups suchas a cyclopentyl group and cyclohexyl group, alkenyl groups such as avinyl group and allyl group and aryl groups such as a phenyl group andtolyl group, and substituted hydrocarbon groups in which at least aportion of the hydrogen atoms within one of the above hydrocarbon groupshave been substituted with a halogen atom such as a chlorine or bromineatom, or a cyano group, such as a cyanomethyl group and trifluoropropylgroup. These substituents must be unreactive. A methyl group, vinylgroup, n-propyl group or phenyl group is preferred. The phenyl groupcontent is particularly important in maintaining a high degree of heatresistance, and relative to the combined total of all the organicsubstituents, the phenyl group content is preferably not less than 40mol %, and is more preferably within a range from 50 to 90 mol %.

The organopolysiloxane has a softening point that is preferably within atemperature range from 40 to 300° C., more preferably from 40 to 230°C., and still more preferably from 40 to 200° C., and is preferably asolid at temperatures not exceeding 40° C., and preferably attemperatures within a range from 0 to 30° C.

In the organopolysiloxane, if the amount of T units is less than 40 mol%, then the organopolysiloxane tends not to be solid at temperatures notexceeding 40° C., and the solubility within organic solvents tends todeteriorate, resulting in either insufficient solubility or eveninsolubility. Further, from the viewpoint of the thermal stabilitydescribed below, the organopolysiloxane of the present inventionpreferably contains no reactive terminal groups such as silanol groupsor hydrolyzable residues. Accordingly, unreactive M units are preferablyintroduced at the terminals, and the amount of those M units ispreferably not less than 1 mol %.

The D units are unreactive structural units that may optionally existwithin the organopolysiloxane, but if the amount of the D units exceeds49 mol %, then the organopolysiloxane tends not to be solid attemperatures not exceeding 40° C., but rather tends to exist as aviscous material having fluidity or even a liquid. As a result, thebonding between the support and the wafer tends to deteriorate,increasing the danger of problems such as misalignment between the waferand the support that constitute the stacked structure during the backsurface grinding or subsequent processing steps.

The M units are unreactive units, the amount of which is typicallywithin a range from 1 to 25 mol %, and preferably from 3 to 20 mol %. Ifthis amount is less than 1 mol %, then ensuring that theorganopolysiloxane has a structure which is soluble in organic solventsand yet has a satisfactorily reduced number of reactive terminal groupssuch as silanol groups and hydrolyzable groups tends to becomedifficult. In contrast, if the amount of M units exceeds 25 mol %, thenthe organopolysiloxane has a structure with a large number of terminalsand a relatively small molecular weight, which is unsuitable.

The organopolysiloxane is essentially unreactive, and even if somemolecular terminals that have not been blocked with unreactive M unitsexist within the molecule, such as terminals having silanol groups orhydrolyzable residues such as an alkoxysilyl group, the amount of thesereactive terminal groups is preferably suppressed to a minimum. Ifsilanol groups or terminal residues such as alkoxysilyl groups existwithin the molecule in large amounts, then cross-linking via acondensation reaction tends to occur when heat is applied, whichdramatically alters the detachability of the substrate and is thereforeundesirable. The total amount of OH groups from silanol groups and ORgroups from alkoxysilyl groups (Si—OR, wherein OR represents an alkoxygroup residue of the alkoxysilane used as a raw material, such as amethoxy group, ethoxy group, n-propoxy group or isopropoxy group),within the entire organopolysiloxane is preferably not more than 4% bymass, and more preferably 2% by mass or less. Introduction of the Munits enables the amount of these types of reactive terminal groups tobe reduced to the desired level. The combination of hydrolyzable groupsand silanol groups is preferably not more than 2% by mass.

The molecular weight of the organopolysiloxane, measured by GPC (gelpermeation chromatography) and reported as a weight-average molecularweight value obtained by using a calibration curve prepared usingstandard polystyrenes (in the present invention, this molecular weightis referred to as the “weight-average molecular weight”) is preferablygreater than 2,000. If this weight-average molecular weight is 2,000 orless, then the organopolysiloxane tends to either not solidify at 10 to20° C., or suffer from inferior heat resistance. The weight-averagemolecular weight is preferably within a range from approximately 3,000to 80,000, and more preferably from approximately 3,000 to 50,000.

Furthermore, in addition to the T units, D units and M units mentionedabove, the organopolysiloxane of the present invention may also comprisesiloxane units represented by SiO_(4/2) (Q units). The amount of these Qunits is preferably within a range from 0.1 to 30 mol %, and morepreferably from 0.2 to 20 mol %.

If the amount of Q units exceeds 30 mol %, then although the producedorganopolysiloxane readily becomes a solid, significant intramolecularcross-linking tends to occur, meaning the solubility in solvents tendsto deteriorate, or control of the softening point within the ideal rangebecomes difficult, either of which is undesirable.

A typical example of an organopolysiloxane of the component (A) thatalso comprises Q units is an organopolysiloxane composed of:

(I) 40 to 98.9 mol % of the above-mentioned T units,

(II) 0 to 48.9 mol % of the above-mentioned D units,

(III) 0.1 to 30 mol % of the above-mentioned Q units, and

(IV) 1 to 25 mol % of the above-mentioned M units.

The organopolysiloxane of the component (A) can be produced usingconventional methods. For example, the organopolysiloxane can beobtained via a hydrolysis-condensation reaction, by mixingorganochlorosilanes and/or organoalkoxysilanes or partialhydrolysis-condensation products thereof that correspond with each ofthe desired siloxane units with a mixed solvent containing a sufficientexcess of water to ensure that all the hydrolyzable groups (such aschlorine atoms and alkoxy groups) are hydrolyzed and an organic solventthat is capable of dissolving the raw material silane compounds and theproduct organopolysiloxane, and then allowing thehydrolysis-condensation reaction to proceed. In order to obtain anorganopolysiloxane with the desired weight-average molecular weight, thereaction temperature and time, and the amounts of water and the organicsolvent can be adjusted as required. Prior to use, the unnecessaryorganic solvent may be removed to produce a powder if required.

—(B) Organic Solvent—

The component (B) is preferably an organic solvent that is capable ofdissolving the organopolysiloxane of the component (A) to form asolution, which can then be applied by a conventional film formationmethod such as spin coating to form a thin film with a thickness of 1 to100 μm. The thickness of this film is more preferably within a rangefrom 5 to 80 μm, and still more preferably from 10 to 60 μm.

Further, organic solvents having a boiling point exceeding 220° C. arenot desirable as they tend to be difficult to volatilize, even duringthe heated drying performed following the coating step, and aretherefore more likely to be retained within the film. This retainedsolvent can cause the formation of gas bubbles at the bonding interfacewhen the bonded structure is exposed to high temperatures during theheating process that is performed following the bonding of thesubstrate.

Specific examples of organic solvents having a boiling point of not morethan 220° C., and preferably within a range from 50 to 220° C., whichcan be used as the component (B) include the solvents listed below, andthe component (B) may be a mixture of two or more of them. Preferably,component (B) is at least one organic solvent selected from the organicsolvents exemplified below.

-   -   Hydrocarbons: pentane, hexane, cyclohexane, decane, isododecane,        limonene    -   Ketones: acetone, methyl ethyl ketone, methyl isobutyl ketone,        cyclopentanone, cyclohexanone    -   Esters: ethyl acetate, butyl acetate, ethyl lactate, ethyl        propionate, propylene glycol monomethyl ether acetate    -   Ethers: tetrahydrofuran, cyclopentyl methyl ether    -   Alcohols: ethanol, isopropanol, butanol, ethylene glycol,        ethylene glycol monomethyl ether, propylene glycol, propylene        glycol monomethyl ether

Of the above solvents, isododecane, cyclopentanone, cyclohexanone,propylene glycol monomethyl ether acetate and propylene glycolmonomethyl ether are ideal.

The organic solvent of the component (B) is used in an amount of from 11to 150 parts by mass, preferably from 25 to 100 parts by mass per 100parts by mass of the organopolysiloxane of the component (A) from theviewpoint of workability and easy formation of an adhesive layer with adesired thickness.

—Other Components—

Besides the component (A) and the component (B) described above, ifrequired, a conventional surfactant or the like may be added to improvethe coating properties of the composition. Specifically, a nonionicsurfactant is preferred, examples of which include a fluorine-basedsurfactant, perfluoroalkyl polyoxyethylene ethanol, fluorinated alkylester, perfluoroalkyl amine oxide or fluorine-containingorganosiloxane-based compound.

Further, in order to further enhance the heat resistance of thecomposition, a conventional antioxidant or a filler such as silica mayalso be added.

<Method of Producing Thin Wafer>

In the method of producing a thin wafer according to the presentinvention, the organopolysiloxane described above is used as theadhesive layer for bonding a wafer having a semiconductor circuit and asupport that is used in reducing the thickness of the wafer. Thethickness of the thin wafer obtained using the production method of thepresent invention is typically within a range from 5 to 300 μm, and moretypically from 10 to 100 μm.

The method of producing a thin wafer according to the present inventionincludes steps (a) to (e) described below.

[Step (a)]

Step (a) comprises bonding the circuit-formed surface of a wafercomprising a circuit-formed surface and a non-circuit-formed surface toa support with an adhesive layer composed of the temporary adhesivecomposition described above disposed therebetween. The wafer comprisinga circuit-formed surface and a non-circuit-formed surface is a wafer inwhich one surface is the circuit-formed surface and the other surface isthe non-circuit-formed surface. The wafer to which the present inventionis applied is typically a semiconductor wafer. Examples of thesemiconductor wafer include not only silicon wafers, but also germaniumwafers, gallium arsenide wafers, gallium phosphide wafers, and aluminumgallium arsenide wafers and the like. Although there are no particularlimitations on the thickness of the wafer, the thickness is typicallywithin a range from 600 to 800 μm, and more typically from 625 to 775μm.

Examples of the support include silicon sheets, glass sheets and quartzsheets and the like. In the present invention, because there is nonecessity to irradiate an energy beam through the support and onto theadhesive layer, the support need not necessarily be formed of alight-transmissive material.

The adhesive layer is a layer composed of the above-described temporaryadhesive composition. The adhesive layer is formed on either one or bothof the circuit-formed surface of the wafer and one surface of thesupport, and the circuit-formed surface of the wafer is then bonded tothe support surface via the adhesive layer. The formation of theadhesive layer on the wafer circuit-formed surface and/or the supportsurface is achieved by applying the above temporary adhesive compositionto the appropriate surface or surfaces, and then drying the compositionto remove the organic solvent of the component (B). The drying istypically performed by heating at a temperature of 80 to 200° C.

The adhesive layer of the present invention is softened by heating. Thetemperature range across which the resin (organopolysiloxane) of theadhesive layer undergoes softening is preferably within a range from 40to 300° C., more preferably from 40 to 230° C., and still morepreferably from 40 to 200° C., and by subjecting the wafer and thesupport to uniform compression under reduced pressure at a temperaturewithin this range, a stacked product comprising the wafer bonded to thesupport is formed. More specifically, a chamber in which the wafer andthe support have been installed is heated, under reduced pressure, to atemperature within the above range, thereby softening or melting theorganopolysiloxane within the adhesive layer, and the wafer and thesupport are then brought into contact and subjected to thermocompressionbonding, thus enabling a uniform bonding interface to be formed withoutthe incorporation of gas bubbles at the bonding interface. During thebonding of the wafer to the support via the adhesive layer, thetemperature of the support is preferably within the temperature rangementioned above. Because the organopolysiloxane within the adhesivelayer undergoes softening at the above bonding temperature, anyirregularities that exist on the surface of the wafer undergoing bondingcan be completely filled, with no voids. The compression applied istypically not more than 63 N/cm², preferably within a range from 1 to 32N/cm², and more preferably from 2 to 23 N/cm². In other words, in thecase of an 8-inch wafer, bonding may be conducted under an applied loadof not more than 20 kN, preferably not more than 10 kN, and morepreferably 7 kN or less.

Commercially available apparatus can be used as the wafer bondingapparatus, and examples include the EVG520IS and 850TB systemsmanufactured by EV Group, and the XBC300 Wafer Bonder manufactured bySUSS MicroTec AG.

[Step (b)]

Step (b) comprises grinding the non-circuit-formed surface of the waferthat has been bonded to the support, namely, grinding the back surfaceon the wafer side of the stacked structure obtained by the bondingperformed in step (a), thereby reducing the thickness of the wafer.There are no particular limitations on the method used for grinding thewafer back surface, and conventional grinding methods may be used. Thegrinding is preferably performed with continuous cooling by applyingwater to the wafer and the grinding stone. Examples of apparatus thatcan be used for the grinding of the wafer back surface include theDAG-810 Grinder manufactured by DISCO Corporation.

[Step (c)]

Step (c) comprises processing the ground non-circuit-formed surface ofthe wafer that has been reduced in thickness by the back surfacegrinding. This step includes a variety of processes used at the waferlevel. Examples of these processes include electrode formation, metalwiring formation and protective film formation and the like. Morespecific examples of the processes include various conventionalprocesses such as metal sputtering which is used for forming electrodesand the like, wet etching which is used for etching metal sputteredlayers, pattern formation by application, exposure and developing of aresist, which is used for forming a mask for metal wiring formation, aswell as resist removal, dry etching, metal plating formation, siliconetching for TSV formation, and oxide film formation on silicon surfacesand the like.

[Step (d)]

Step (d) comprises detaching the wafer that has been processed in step(c) from the support, namely, detaching the reduced thickness wafer thathas been subjected to a variety of processes from the support prior todicing of the wafer. Although there are no particular limitations on thedetachment method employed, the main examples include methods thatcomprise heating the wafer and the support while sliding the wafer andthe support in opposing horizontal directions to achieve detachment,methods that comprise securing either the wafer or the support of thestacked structure horizontally and then heating the structure while theother non-secured component is lifted off at a predetermined angle fromthe horizontal, and methods that comprise bonding a protective film tothe ground surface of the wafer and subsequently peeling the wafer andthe protective film away from the support.

In the present invention, any of these detachment methods may beemployed, but the horizontal slide detachment method is particularlysuitable. In this method, the stacked structure is heated, and when theadhesive layer has reached a melted or softened state, a horizontalforce is applied to detach the wafer from the support. For the adhesivesused in the present invention, the heating temperature is preferablywithin a range from 50 to 300° C., more preferably from 60 to 230° C.,and still more preferably from 70 to 200° C.

Examples of apparatus that can be used for performing this detachmentinclude the EVG850 DB system manufactured by EV Group, and the XBC300Wafer Bonder manufactured by SUSS MicroTec AG.

[Step (e)]

The step (e) comprises removing residual adhesive from thecircuit-formed surface of the detached wafer. This removal of residualadhesive can be achieved, for example, by cleaning the wafer.

In the step (e), any cleaning liquid that is capable of dissolving theorganopolysiloxane within the adhesive layer can be used, and specificexamples of the cleaning liquid include ketones such as acetone,cyclopentanone, cyclohexanone, 2-butanone, methyl isobutyl ketone,2-heptanone and 2-octanone, esters such as butyl acetate, methylbenzoate and γ-butyrolactone, cellosolves such as butyl cellosolveacetate, propylene glycol monomethyl ether and propylene glycolmonomethyl ether acetate, amides such as N,N-dimethylformamide,N,N-dimethylacetamide and N-methyl-2-pyrrolidone, and alcohols such asisopropanol and butanol. Among these, ketones, esters, cellosolves andalcohols are preferred, and propylene glycol monomethyl ether, propyleneglycol monomethyl ether acetate, n-methyl-2-pyrrolidone, acetone,cyclopentanone, cyclohexanone, 2-butanone, methyl isobutyl ketone andisopropanol are particularly desirable. These solvents may be usedindividually or in mixtures containing two or more different solvents.Further, in those cases where removal of the residual adhesive provesdifficult, a base or acid may be added to the solvent if required.Examples of bases that may be added include amines such as ethanolamine,diethanolamine, triethanolamine, triethylamine and ammonia, and ammoniumsalts such as tetramethylammonium hydroxide. Examples of acids that maybe used include organic acids such as acetic acid, oxalic acid,benzenesulfonic acid and dodecylbenzenesulfonic acid. The amount addedof the acid or base, reported as a concentration within the cleaningliquid, is typically within a range from 0.01 to 10% by mass, andpreferably from 0.1 to 5% by mass. Further, in order to further improvethe removability of the residue, a conventional surfactant may also beadded to the cleaning liquid. Examples of the cleaning method employedinclude puddle cleaning methods using the liquid described above, spraycleaning methods, and methods that involve immersion in a tankcontaining the cleaning liquid. Cleaning is typically performed at atemperature of 10 to 80° C., and preferably 15 to 65° C.

EXAMPLES Synthesis of Organopolysiloxanes Preparation Example 1

A 1 L flask fitted with a stirrer, a cooling device and a thermometerwas charged with 234 g (13 mols) of water and 35 g of toluene, and theflask was then heated to 80° C. in an oil bath. A dropping funnel wascharged with 148 g (0.7 mols) of phenyltrichlorosilane, 51 g (0.20 mols)of diphenyldichlorosilane and 9 g (0.1 mols) of trimethylchlorosilane,and the resulting mixture in the dropping funnel was then added dropwiseto the flask with constant stirring over a period of one hour. Followingcompletion of the dropwise addition, the reaction mixture was stirredfor a further one hour at 80° C. Subsequently, the reaction mixture wasleft to settle while cooling to room temperature, the separated waterphase was removed, and then a water washing operation, in which a 10% bymass aqueous solution of sodium sulfate was mixed with the toluene phasefor 10 minutes, the resulting mixture was left to settle for 30 minutes,and the separated aqueous phase was then removed, was repeated until thetoluene phase was neutral, thereby halting the reaction. An esteradapter was then connected to the flask, and the toluene phasecontaining the organopolysiloxane was heated under reflux to removeresidual water from the toluene phase. Once the temperature inside theflask had reached 110° C., the reflux was continued for a further onehour, and the toluene solution was then cooled to room temperature. Thethus obtained organopolysiloxane solution was filtered to removeimpurities, and the toluene was then removed by distillation underreduced pressure, yielding 125 g of a solid organopolysiloxane (resin1).

The obtained organopolysiloxane comprised 70 mol % of T units, 20 mol %of D units and 10 mol % of M units, 79 mol % of the organic substituentson the Si atoms were phenyl groups, the terminals included 0.03 mols ofsilanol groups per 100 g of the organopolysiloxane, the externalappearance was of a colorless transparent solid, and the weight-averagemolecular weight was 9,600. Further, the softening point of the resinwas 90° C.

Preparation Example 2

An apparatus was setup in a similar manner to Preparation Example 1, the1 L flask was charged with 234 g (13 mols) of water and 35 g of toluene,and the flask was then heated to 80° C. in an oil bath. With theexception of charging the dropping funnel with 116 g (0.55 mols) ofphenyltrichlorosilane, 51 g (0.2 mols) of diphenyldichlorosilane, 13 g(0.1 mols) of dimethyldichlorosilane and 16 g (0.15 mols) oftrimethylchlorosilane, preparation was conducted in the same manner asPreparation Example 1, yielding 132 g of a solid organopolysiloxane(resin 2).

The thus obtained organopolysiloxane comprised 55 mol % of T units, 30mol % of D units and 15 mol % of M units, 59 mol % of the organicsubstituents on the Si atoms were phenyl groups, the terminals included0.02 mols of silanol groups per 100 g of the organopolysiloxane, theexternal appearance was of a colorless transparent solid, and theweight-average molecular weight was 11,200. Further, the softening pointof the resin was 78° C.

Preparation Example 3

An apparatus was setup in a similar manner to Preparation Example 1, the1 L flask was charged with 234 g (13 mols) of water, 35 g of toluene and1 g of methanesulfonic acid, and the flask was then heated to 80° C. inan oil bath. With the exception of subsequently charging the droppingfunnel with 119 g (0.6 mols) of phenyltrimethoxysilane, 24 g (0.1 mols)of diphenyldimethoxysilane, 6 g (0.05 mols) of dimethyldimethoxysilane,15 g (0.1 mols) of tetramethoxysilane and 16 g (0.15 mols) oftrimethylmethoxysilane, preparation was conducted in the same manner asPreparation Example 1, yielding 123 g of a solid organopolysiloxane(resin 3).

The thus obtained organopolysiloxane comprised 60 mol % of T units, 15mol % of D units, 10 mol % of Q units and 15 mol % of M units, 59 mol %of the organic substituents on the Si atoms were phenyl groups, theterminals included 0.04 mols of silanol groups per 100 g of theorganopolysiloxane, the external appearance was of a colorlesstransparent solid, and the weight-average molecular weight was 10,200.Further, the softening point of the resin was 110° C.

Comparative Preparation Example 1

An apparatus was setup in a similar manner to Preparation Example 1, the1 L flask was charged with 234 g (13 mols) of water and 35 g of toluene,and the flask was then heated to 80° C. in an oil bath. With theexception of charging the dropping funnel with 53 g (0.25 mols) ofphenyltrichlorosilane, 101 g (0.4 mols) of diphenyldichlorosilane, 32 g(0.25 mols) of dimethyldichlorosilane and 11 g (0.1 mols) oftrimethylchlorosilane, preparation was conducted in the same manner asPreparation Example 1, yielding 143 g of a highly viscousorganopolysiloxane (comparative resin 1).

The thus obtained organopolysiloxane comprised 25 mol % of T units, 65mol % of D units and 10 mol % of M units, 57 mol % of the organicsubstituents on the Si atoms were phenyl groups, the terminals included0.01 mols of silanol groups per 100 g of the organopolysiloxane, theexternal appearance was of a colorless transparent solid, and theweight-average molecular weight was 11,700. This resin exhibitedfluidity at room temperature, but the softening point of a solid sampleprepared by cooling was 23° C.

Comparative Preparation Example 2

An apparatus was setup in a similar manner to Preparation Example 1, the1 L flask was charged with 234 g (13 mols) of water and 35 g of toluene,and the flask was then heated to 80° C. in an oil bath. With theexception of charging the dropping funnel with 137 g (0.65 mols) ofphenyltrichlorosilane, 63 g (0.25 mols) of diphenyldichlorosilane and 13g (0.1 mols) of dimethyldichlorosilane, preparation was conducted in thesame manner as Preparation Example 1, yielding 123 g of a solidorganopolysiloxane (comparative resin 2).

The thus obtained organopolysiloxane comprised 65 mol % of T units and35 mol % of D units, 85 mol % of the organic substituents on the Siatoms were phenyl groups, the terminals included 0.3 mols of silanolgroups per 100 g of the organopolysiloxane, the external appearance wasof a colorless transparent solid, and the weight-average molecularweight was 8,200. Further, the softening point of the resin was 83° C.

The compositions and the weight average molecular weights of the resinsobtained in the preparation examples and comparative preparationexamples above are shown in Table 1.

Examples 1 to 3, Comparative Examples 1 to 2

Using a solution prepared by dissolving the organopolysiloxane (resins 1to 3 and comparative resins 1 and 2) in a solvent shown in Table 2 at aconcentration shown in Table 2, an adhesive layer having a (dried)thickness shown in Table 2 was formed by spin coating across the entiresurface of one side of an 8-inch silicon wafer (thickness: 725 μm).Using a glass sheet with a diameter of 8 inches as a support, thissupport and the silicon wafer having the adhesive layer formed thereonwere then bonded together inside a vacuum bonding apparatus under theconditions shown in Table 2, thus preparing a stacked product.

Subsequently, the tests described below were performed. Further,separate test substrates were also prepared to evaluate thedetachability and the cleaning removability of the resins. The resultsare shown in Table 2.

—Adhesion Test—

Bonding of the 8-inch wafer was performed using a Wafer Bonding System520IS manufactured by EV Group. The bonding was performed at the bondingtemperature shown as “Bonding temperature” in Table 2, at an internalchamber pressure during bonding of not more than 10⁻³ mbar, and under aloading of 5 kN. Following bonding, the stacked structure was cooled toroom temperature, and the state of adhesion at the bonding interface wasinspected visually. In those cases where no anomalies such as gasbubbles had occurred at the interface, the adhesion was evaluated asgood and was recorded using the symbol O, whereas in those cases whereanomalies were detected, the adhesion was evaluated as poor and wasrecorded using the symbol x

—Back Surface Grinding Durability Test—

Grinding of the back surface of the silicon wafer was conducted using agrinder (DAG810, manufactured by DISCO Corporation). Following grindingdown to a final substrate thickness of 50 μm, the wafer was inspectedunder an optical microscope for the existence of anomalies such ascracking or detachment. In those cases where no anomalies had occurred,the grinding durability was evaluated as good and was recorded using thesymbol O, whereas in those cases where anomalies were detected, thegrinding durability was evaluated as poor and was recorded using thesymbol x.

—Heat Resistance Test—

A stacked structure in which the silicon wafer had been subjected toback surface grinding was placed inside an oven at 250° C. under anitrogen atmosphere for two hours, and was then heated on a hot plate at270° C. for 10 minutes and inspected for the existence of externalappearance anomalies. In those cases where no external appearanceanomalies had occurred, the heat resistance was evaluated as good andwas recorded using the symbol O, whereas in those cases where externalappearance anomalies were detected, the heat resistance was evaluated aspoor and was recorded using the symbol x.

—Detachability Test—

The detachability of a substrate was evaluated in a simulated mannerusing the test described below.

The adhesive layer described above was formed on a separate 6-inchsilicon wafer, and with the wafer undergoing heating on a hot plate atthe temperature as “Bonding temperature” shown in Table 2, a siliconsubstrate that had been cut into a fragment with dimensions of 35 mm×35mm×thickness: 0.725 mm (hereinafter referred to as the “siliconfragment”) was pressed onto and bonded to the wafer. Subsequently, thestacked structure was exposed to the same conditions as theabove-described heat resistance test, and a bond tester (series 4000,manufactured by DAGE Precision Industries Ltd.) was used to perform adetachability test described below.

FIG. 1 is a diagram illustrating the method used in the detachabilitytest. As illustrated in FIG. 1, a test piece composed of a silicon wafer1, an adhesive layer 2 formed on top of the silicon wafer 1, and asilicon fragment 3 bonded to the silicon wafer 1 via the adhesive layer2 was secured to a heater 4 fitted with a vacuum chuck. With the testpiece being heated at 180° C., a probe 5 of the above-mentioned bondtester was moved in the direction of the arrow 6 and pressed against theside of the silicon fragment 3 in a horizontal direction. The size ofthis pressing force was gradually increased, and the force at the pointwhere the silicon fragment 3 started to slide was measured. In thosecases where the silicon fragment started to slide at a horizontalpressing force of not more than 1 N, the detachability was evaluated asgood and was recorded using the symbol O, whereas in those cases where aforce exceeding 1 N was required, the detachability was evaluated aspoor and was recorded using the symbol x.

—Cleaning Removability Test—

A stacked product was prepared using a separate 8-inch wafer in the samemanner as that prepared and subjected to the adhesion test, etc. above,and then to heat treatment under the same conditions as in the heatresistance test described above. Thereafter, the wafer was debonded fromthe glass sheet in a sliding fashion at 180° C. with a debonding system(EVG805). The side debonded from the glass sheet of the wafer has aremaining adhesive layer. The wafer thus obtained was subjected to thefollowing cleaning removability test.

The wafer was secured on a spin coater with the adhesive layer facingupward, and propylene glycol monomethyl ether was sprayed onto the waferas a cleaning solvent. The propylene glycol monomethyl ether was left tosit on the wafer for two minutes at 23° C. and was then removed byrotating the coater, and this operation of spraying propylene glycolmonomethyl ether onto the wafer and leaving it to sit for two minuteswas repeated a further two times. Subsequently, with the wafer beingspun, isopropyl alcohol (IPA) was sprayed on to the wafer to perform arinse. Subsequently, the external appearance of the wafer was inspectedvisually for the presence of residual adhesive resin. In those caseswhere no resin residues were detected, the cleaning removability wasevaluated as good and was recorded using the symbol O, whereas in thosecases where resin residues were detected, the cleaning removability wasevaluated as poor and was recorded using the symbol x.

TABLE 1 Comparative Comparative Preparation Preparation PreparationPreparation Preparation example 1 example 2 Example 1 Example 2 Example3 Comparative Comparative Resin 1 Resin 2 Resin 3 resin 1 resin 2 Tunits 70 55 60 25 65 (mol %) D units 20 30 15 65 35 (mol %) M units 1015 15 10 — (mol %) Q units — — 10 — — (mol %) Weight-average 9,60011,200 10,200 11,700 8,200 molecular weight

TABLE 2 Comparative Comparative Example 1 Example 2 Example 3 example 1example 2 Resin 1 70 — — — — Resin 2 — 60 — — — Resin 3 — — 65 — —Comparative resin 1 — — — 75 — Comparative resin 2 — — — — 65Cyclopentanone 30 30 — — 35 PGMEA (*) — 10 35 25 — Thickness (μm) 20 3020 20 20 Bonding temperature 140° C. 160° C. 170° C. 140° C. 160° C.Adhesion ◯ ◯ ◯ ◯ ◯ Back surface grinding ◯ ◯ ◯ X ◯ durability Heatresistance ◯ ◯ ◯ — X Detachability ◯ ◯ ◯ — X Cleaning removability ◯ ◯ ◯— X (Note: PGMEA (*) = propylene glycol monomethyl ether acetate)

INDUSTRIAL APPLICABILITY

The temporary adhesive composition of the present invention is useful,for example in the field of semiconductor production, for achievingtemporary adhesion between wafers or between a wafer and a support, suchas the case where the circuit-formed surface of a semiconductor wafer isbonded to a support while the non-circuit-formed surface of the wafer issubjected to grinding, and the support is then readily detachedfollowing completion of the grinding.

1. A temporary adhesive composition comprising: (A) anorganopolysiloxane comprising: (I) 40 to 99 mol % of siloxane unitsrepresented by R¹SiO_(3/2) (T units), (II) 0 to 49 mol % of siloxaneunits represented by R²R³SiO_(2/2) units (D units) and (III) 1 to 25 mol% of siloxane units represented by R⁴R⁵R⁶SiO_(1/2) units (M units),wherein each of R¹ to R⁶ represents an unsubstituted or substitutedmonovalent hydrocarbon group of 1 to 10 carbon atoms, and having aweight-average molecular weight exceeding 2,000, and (B) an organicsolvent having a boiling point of not more than 220° C.
 2. Thecomposition according to claim 1, wherein the organopolysiloxane ofcomponent (A) is composed of: (I) 40 to 98.9 mol % of the T units, (II)0 to 48.9 mol % of the D units, (III) 0.1 to 30 mol % of siloxane unitsrepresented by SiO_(4/2) (Q units), and (IV) 1 to 25 mol % of the Munits.
 3. The composition according to claim 1, wherein each of R¹ to R⁶represents a methyl group, vinyl group, n-propyl group or phenyl group.4. The composition according to claim 1, wherein relative to thecombined total of all the organic substituents in the organopolysiloxaneof component (A), the phenyl group content is not less than 40 mol %. 5.The composition according to claim 1, wherein relative to the combinedtotal of all the organic substituents in the organopolysiloxane ofcomponent (A), the phenyl group content is within a range from 50 to 90mol %.
 6. The composition according to claim 1, wherein theorganopolysiloxane of component (A) has a softening point that is withina temperature range from 40 to 300° C., and is a solid at temperaturesnot exceeding 40° C.
 7. The composition according to claim 1, whereinthe weight-average molecular weight is within a range from 3,000 to80,000.
 8. The composition according to claim 1, wherein the organicsolvent of component (B) is a hydrocarbon, ketone, ester, ether,alcohol, or a mixture of two or more thereof.
 9. The compositionaccording to claim 1, wherein the organic solvent of component (B) isisododecane, cyclopentanone, cyclohexanone, propylene glycol monomethylether acetate, propylene glycol monomethyl ether or a mixture of two ormore thereof.
 10. The composition according to claim 1, wherein theorganic solvent of component (B) is present in an amount of 11 to 150parts by mass per 100 parts by mass of the organopolysiloxane ofcomponent (A).
 11. A method of producing a thin wafer, the methodcomprising: (a) bonding a circuit-formed surface of a wafer having thecircuit-formed surface and a non-circuit-formed surface to a supportwith an adhesive layer composed of the temporary adhesive compositiondefined in claim 1 disposed therebetween, (b) grinding thenon-circuit-formed surface of the wafer bonded to the support, (c)processing the non-circuit-formed surface of the wafer that hasundergone grinding of the non-circuit-formed surface, (d) detaching theprocessed wafer from the support, and (e) removing residual adhesivecomposition from the circuit-formed surface of the detached wafer.